Radio communication systems are used for transmission of information, voice or data with the aid of electromagnetic waves over a radio interface, also called an air interface, between a sending and a receiving radio station. An example of a radio communication system is the known GSM mobile radio system as well as its further development with the packet data service GPRS or EDGE, of which the network architecture is described for example in B. Walke, Mobilfunknetze und ihre Protokolle (Mobile Radio Networks and their Protocols), Volume 1, Teubner-Verlag Stuttgart, 1998, Pages 138 to 151 and Pages 295 to 311. In this case a channel formed from a narrowband frequency range and a time slot is provided in each case for transmission of a subscriber signal. Since a subscriber signal in a channel differs in frequency and time from the remaining subscriber signals, the radio station can detect the data of the subscriber signal. In new radio communication systems, for example the UMTS system, the individual subscribers are additionally differentiated by different spread codes.
With packet-switched data transmission the data is transmitted for a number of subscribers over one and the same physical channel. In the GPRS or EDGE systems which are currently the norm a number, for example six, physical channels, which are designated as packet data channels, are provided for packet switched data transmission. Each subscriber can in these systems also occupy a number of these packet data channels simultaneously (multislot). Depending on the subscriber, a packet data flow (Temporary Block Flow TBF) is broken down in such cases into time-limited radio blocks which are transmitted. In this case different modulation/coding schemes are applied to give error protection. The possible modulation/coding schemes differ as regards the subdivision of the radio block into useful load and error-protection information. Depending on the modulation/coding scheme set, these radio blocks have a different useful load but the same length. Depending on the radio conditions a connection is assigned a modulation/coding scheme with greater or lower error protection. If radio conditions are bad, a modulation/coding scheme with a greater level of protection against errors and if conditions are good a modulation/coding scheme with a lower level of error protection is assigned. Since the proportion of the useful load differs depending on the modulation/coding scheme used, the data rates which can be achieved also differ.
For packet data switching a radio communication system for example comprises a GSM mobile radio network with GPRS, a multiplicity of Serving GPRS Support Nodes (SGSN) which are internetworked and which establish the access to a fixed data network. The Serving GPRS Support Nodes are further connected to Base Station Controllers (BSC). Each Base Station Controller in its turn makes possible at least one connection to at least one Base Station (BTS) and handles the administration of the technical resources of the base stations connected to it. For administration of the radio technical resources for packet switched data transmission the base station controller includes a Packet Control Unit (PCU). A base station is a transceiver unit which can establish a communication link to a mobile station over a radio interface. The individual subscribers are allocated on a channel for packet-switched data transmission via the packet control unit.
After the data arrives in the packet control unit PCU this is transmitted via what is referred to as the Abis interface to the base station, encoded there and sent over the air interface to the mobile station. The Abis interface is a PCM30 connection with a data rate of 64 Kbit/s, which is divided up into four subchannels each of 16 Kbit/s. Thus one constant-length data packet per time slot is transmitted on the Abis interface. Since, depending on the modulation/coding scheme used, different useful data rates are available to a user on the radio interface, a different quantity of time slots is required on the Abis interface for the further transmission of this data, depending on the modulation/coding scheme used. So that a subscriber who obtains a high data rate via the radio interface can use this high data rate, it must therefore be possible at the Abis interface to allocate a sufficient quantity of time slots accordingly. One option for avoiding a bottleneck when undertaking this allocation is to design the Abis interface so that for each subscriber, independent of the modulation/coding scheme actually used, the number of time slots required for the highest data rate is reserved. This leads to inefficient utilization of the line capacity however.
An arrangement of transmission channels of an Abis interface in a cellular radio network is known from US 2002/0003783 A1. In this patent publication, a prespecified number of transmission channels is permanently allocated to operations and signaling on a base-station-specific basis. A required number of transmission channels is allocated dynamically to a packet data transmission, with a quantity of packet data being varied depending on a modulation and with a coding scheme of a Um interface.
The underlying problem is thus that of finding a method for allocating radio technical resources for packet-switched data transmission in which on the one hand satisfactory data rates are guaranteed for all subscribers and on the other hand the available infrastructure resources can be used effectively.